Gene therapy approaches are often hampered by low transduction efficiencies of target cells by recombinant viral vectors. Retroviral vectors, and in particular human immunodeficiency virus 1 (HIV-1)-based lentiviral vectors (LVs) are promising vehicles for gene therapy (D'Costa et al., 2009). These vectors are used currently in clinical applications to treat various diseases such as immune deficiencies, neurodegenerative or neurological diseases, anemias, HIV infection. Some of the applications of retroviral vectors rely on the transduction of specific target cells ex vivo such as hematopoietic stem/progenitor cells expressing the CD34 marker. A limiting factor with the use of recombinant lentiviral particles, is the capacity to obtain highly infectious titers during production of recombinant lentiviral vector particles. One way to circumvent this limitation is to concentrate the viral supernatant during the purification steps (Rodrigues et al., 2007). However, purification protocols are difficult to establish for some LVs, depending on the envelope glycoproteins used to pseudotype viral particles as it is the case for GALVTR-LVs (LVs pseudotyped with gibbon ape leukemia virus envelope glycoprotein fused to the cytoplasmic tail of the amphotropic murine leukemia virus (MLV-A) envelope glycoprotein (Sandrin et al., 2002)). Therefore, many lentiviral vector preparations have low titer and transduction efficacy is limited. Another limiting factor is the ability of the lentiviral vector itself to infect target cells. Several envelope glycoproteins such as VSV-G, RD114TR, GALVTR can be used to pseudotype lentiviral vectors and have variable infectivity on target cells such as CD34+ cells (Sandrin et al., 2002). One strategy to circumvent these limitations is the addition of cofactors to optimize transduction protocols like cationic polymers (e.g. polybrene) or fibronectin fragments (e.g. retronectin) (Davis et al., 2004; Pollok et al., 1999). U.S. Pat. No. 7,759,467 describes a method for increasing the efficiency of transduction of hematopoietic cells by retroviruses comprising the infection of the cells in the presence of fibronectin or fibronectin fragments. However, the proposed method is not totally satisfactory for at least two reasons. First, the fragments of fibronectin used for improving the efficiency of retroviruses present significant economic drawbacks since they usually comprise around 270 or more amino acids. Furthermore, the use of fibronectin or fibronectin fragments requires coating of the culture plates and preloading of viral supernatants onto immobilized fibronectin fragments. These two steps are difficult to standardize and can lead to some saturation of target cell transduction depending on the concentrations of fibronectin fragments and viral supernatants used (Novelli et al., 1999).
Interestingly, natural cationic peptides called SEVI have been recently identified in human semen as strong enhancers of HIV-1 infectivity (Munch et al., 2007; Roan et al., 2009). This family of peptides has also been disclosed in international application No. PCT/EP2007/050727, which describes fragments of amino acid residues 240-290 of human prostatic acid phosphatase which promote viral infection of a cell.
International application No. PCT/FR02/01772 describes amphipathic cationic peptides having an absolute charge higher than or equal to 2 at pH 7.4 and comprising at least one hydrophilic portion, said portion comprising at least three residues which are capable of being protonized at a pH of less than 7.4 in order to transfer a nucleic acid or a protein in a cell. This document does not describe or suggest the use of such peptides for improving the transduction efficiency of a virus or viral vector. Furthermore, these amphipathic cationic peptides harbor antibiotic activities (Mason et al., 2009).
The aim of the inventors was to provide means for improving the transduction efficiency of a virus or viral vector, for example for improving delivery of a gene into target cells. Since peptides are interesting for their biodegradable property, for their reduced size, simplicity of characterization and large-scale production, extensive research has been conducted for identifying alternatives to fibronectin and SEVI peptides.